Controls on mass loss and nitrogen dynamics of oak leaf litter along an urban-rural land-use gradient

Abstract

Using reciprocal leaf litter transplants, we investigated the effects of contrasting environments (urban vs. rural) and intraspecific variations in oak leaf litter quality on mass loss rates and nitrogen (N) dynamics along an urban-rural gradient in the New York City metropolitan area. Differences in earthworm abundances and temperature had previously been documented in the stands along this gradient. Red oak leaf litter was collected and returned to its original source stand as native litter to measure decay rates along the gradient. To separate site effects from litter quality effects on decay, reciprocal transplants of litter were also made between stands at the extremes of the environmental gradient (urban and rural stands). Land-use had no effect on mass loss and N dynamics of native litter by the end of the 22-month incubation period. The lack of differences in native litter suggests the factors affecting decay were similar across the stands in this study. However, in the transplant study both environment and litter type strongly affected decay of oak leaf litter. On average urban and rural litter decomposed faster over the incubation period in urban than in rural stands (P=0.016 and P=0.001, respectively, repeated measures ANOVA). Differences in mass loss between urban and rural stands resulted in rural environments having less mass remaining than urban environments at the end of the incubation period (25.6 and 46.2% for urban and rural sites, respectively). Likewise, less N remained in leaf residue in urban sites (71.3%) compared to that in rural sites (115.1%). Litter type also affected mass loss rates during the 22-month incubation period. On average rural litter mass loss rates were faster than urban litter rates in both urban and rural stands (P=0.030 and P=0.026, respectively, repeated measures ANOVA). By the end of the incubation period, rural litter exhibited 43 and 20% greater mass loss and retained 44 and 5% less N than urban litter decomposing in the same urban and rural sites, respectively. These results suggest that different factors were controlling mass loss and N release rates along this urban-rural gradient. In urban stands, exotic earthworms and warmer temperatures may be compensating for what would otherwise be slowly decaying leaf litter because of its lower quality. Likewise, the lower quality litter produced in the urban stands may be decreasing the net release of N from litter despite higher temperatures and earthworm activity. Even though native litter decay rates were similar, the differential importance of the factors affecting decay along this gradient could alter the response of these forests to disturbance and variations in climate.

Decomposition of tree leaf litter on pavement: implications for urban water quality

“…For example, rates of decomposition in this study were in the range of those measured in urban forest stands in warmer regions (e.g., the eastern United States) Pouyat and Carreiro 2003;Pavao-Zuckerman and Coleman 2005). The rapid initial rates of decomposition seen here were more rapid than initial decomposition rates of litter of congeners measured in an urban stream in the eastern United States (Swan et al 2008) and were similar to rates measured in Australian urban streams for litter with high carbon quality (Imberger et al 2008).…”

“…Litter P concentrations were similar between urban and natural area congeners. Second, temperatures are higher in the urban area (especially on road surfaces) than in the surrounding region because of urban heat island effects, perhaps stimulating decomposition (Pouyat and Carreiro 2003). Third, in contrast to our initial expectation that lack of nutrient sources and decomposer microbes might limit decomposition rates in the gutter, we observed a number of potential nutrient and microbial sources to the street gutter that could have fueled rapid decomposition.…”

“…McDonnell et al 1997) and on the effects of urban pollution on litter chemistry and decomposability (Fritze 1988;Cotrufo et al 1995;Carreiro et al 1999). When comparing decomposition rates among forest stands of similar age and composition across urban to rural gradients, these studies found that decomposition rates were sometimes more rapid in the urban environment, likely because of warmer temperatures and more earthworms in urban stands Pouyat and Carreiro 2003). Similarly, decomposition can be more rapid in urban streams likely because of higher temperatures and greater nutrient availability (Imberger et al 2008).…”

European aspen and hybrid aspen under changing environment – Leaf traits, growth and litter decomposition

“…can account for the faster decay of urban litter and the slower decay of motorway litter. Our results contrast with some previous studies comparing the decomposability of urban and rural leaf litter (Cotrufo et al 1995, Carreiro et al 1999, Pouyat and Carreiro 2003, which were, however, conducted on more xeromorphic Quercus species.…”

Earthworm, microbial biomass, and leaf litter decay responses after invasive honeysuckle shrub removal from urban woodlands.

“…As has been reported in other studies, the activity of earthworms and other soil macroinvertebrates can greatly enhance the decomposition of leaf litter (Pouyat and Carreiro 2003;Suárez et al 2006;Heneghan et al 2007;Holdsworth et al 2008).…”